root:
             product   file:plan.py
             product   step:./plan.py

file:plan.py
               state = CONFIRMED
             creator   root:
                sink   step:./plan.py

step:./plan.py
               state = SUCCEEDED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py
             product   step:cat src2.txt

(step:cat src1.txt)
               state = PENDING
                need = DEFAULT
              source   (file:src1.txt)

(file:src1.txt)
               state = UNDECLARED
                sink   (step:cat src1.txt)

step:cat src2.txt
               state = PENDING
                need = DEFAULT
             creator   step:./plan.py
              source   (file:src2.txt)

(file:src2.txt)
               state = UNDECLARED
                sink   step:cat src2.txt
